1. Field of the Invention
The present invention relates to a roll replacing method and a roll replacing system for a chockless rolling mill which rolls a band plate such as a steel plate.
2. Description of the Related Art
Among rolling mills for hot rolling a band plate such as a steel plate, there is a rolling mill of the type shown in Japanese Unexamined Patent Publication No. 229605/96. FIGS. 10 to 11 show this type of rolling mill. An outline of this type of rolling mill will be described by reference to FIGS. 10 to 11.
In FIGS. 10 to 11, a pair of housings 2 for supporting work rolls are placed facing each other on a pair of base blocks 1. On each housing 2, two bushes 3 for eccentrically supporting the work rolls are rotatably provided via bearing metals so as to be in agreement with two axes arranged vertically parallel along the direction in which the housings are opposed to each other. The rotary bush 3 has one end protruding outward of the housing 2. On the protruding outer periphery of the rotary bush 3, a worm wheel 4 is provided. O.sub.1 is a center of rotation of the rotary bush 3.
On the outer wall surfaces of the housings 2 near the worm wheels 4, drive motors 5 are provided. On a drive shaft 5a of each drive motor 5, a worm 6, meshing with the worm wheel 4, is provided.
On each rotary bush 3, a bearing 7 for supporting the work roll, which has a center of rotation O.sub.2, is provided at an eccentric position spaced by a tiny distance from the center of rotation O.sub.1 of the rotary bush 3. Shaft portions 8a and 9a at both ends of the pair of upper work roll 8 and lower work roll 9, are supported by the bearings 7.
When the drive motor 5 is actuated, the upper work roll 8 is turned upwardly eccentrically, and the lower work roll 9 is turned downwardly eccentrically, at a suitable angle of rotation. Thus, an arbitrary roll gap G is established between the upper and lower work rolls 8 and 9, so that a band plate 10 is passed through the roll gap G, and rolled thereby.
The above-described type of rolling mill has a structure without a bearing box which can be removed together with rolls, i.e., a roll chock, as in earlier technologies. This type of rolling mill will be called a chockless rolling mill hereinbelow.
Generally, the work rolls of rolling mill have a roll surfaces roughened and worn by a rolling operation. When the rolls are surface-roughened, the rolling line is stopped, and the surface-roughened rolls are replaced by polished spare rolls (or fresh rolls). Then, the rolling operation is performed again, by the fresh rolls, while the removed rolls are being polished. This procedure is repeated. The rolls are replaced several times everyday.
With the aforementioned chockless rolling mill, when the housing 2 is fixed to the line, the work rolls 8, 9 and the bearings 7 cannot be removed from the housing 2, when replacing the rolls, because of the structure of the rolling mill. Thus, this type of rolling mill requires that roll replacement be performed by a method as illustrated in FIG. 12. In FIG. 12, M.sub.1 denotes a chockless rolling mill being used on a hot rolling line, M.sub.2 and M.sub.3 denote two spare chockless rolling mills of the same structure, Ds denotes a drive side of the rolling line, and Ws denotes a work side of the rolling line.
The rolls are replaced in the following manner: When the rolls 8, 9 of the rolling mill M.sub.1, placed on the line, are surface-roughened, the entire rolling mill M.sub.1 is pulled out to an M.sub.1 ' position indicated by a one-dot chain line at the work side of the rolling line. Immediately thereafter, the spare chockless rolling mill M.sub.2 is assembled onto the rolling line. The removed rolling mill M.sub.1 is laid horizontally so that the upper and lower rolls 8 and 9 will lie horizontally. The rolls 8, 9 are supported on a horizontal base, while the respective housings 2 on the drive side Ds and the work side Ws are suspended by cranes, detached horizontally from the rolls, and kept in that position temporarily.
The detached rolls 8, 9 on the base are polished with a polishing machine, and assembled to the housings 2 on the drive side Ds and the work side Ws in the same manner as described above. The assembly is placed on standby as a spare rolling mill M.sub.1.
According to the foregoing conventional roll replacing method for a rolling mill, the heavy body of the rolling mill is handled in a suspended manner for roll removed and mounting. It takes a long time to removed the rolls from the body of the rolling mill, polish them, and mount them, thus completing repair. A single spare rolling mill M.sub.2 is not enough, because replacement of the rolls cannot be completed before the next replacement of the rolling mill M.sub.2 on the rolling line needs to be carried out. Thus, two or three spare rolling mills become necessary, thus the facility cost.